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    <script>
        let arr1 = [1,2,3];
        let arr2 = [4,5,6];

        // concat
        let arr3 = arr1.concat(arr2);

        // 扩展运算符
        let arr4 = [...arr1,...arr2];

        // flat()扁平化处理
        let arr5 = [arr1,arr2].flat();

        console.log(arr3,arr4,arr5);
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